The top 10 Republican presidential contenders hold their third debate Wednesday in Boulder, Colorado.

The debate will be broadcast by CNBC and the focus is expected to be on the top four candidates in the Republican field, according to the latest national polls: real estate mogul Donald Trump, retired neurosurgeon Ben Carson, Florida Senator Marco Rubio and former Florida Governor Jeb Bush.

The stakes seem especially critical for Bush, who recently slashed campaign spending after slipping further behind in national polls and surveys in key early voting-states such as Iowa, New Hampshire and South Carolina.

Bush was busy this past weekend trying to reassure wealthy campaign donors at a Houston retreat.

An earlier debate will also be held featuring four other contenders who did not make the top 10: Former Pennsylvania Senator Rick Santorum, Louisiana Governor Bobby Jindal, former New York Governor George Pataki and South Carolina Senator Lindsey Graham.

Former Virginia Governor Jim Gilmore did not qualify for the earlier debate because he is below 1 percent in the polls.

The size of the Republican field is a major contrast with the Democratic race where only three contenders remain: former Secretary of State Hillary Clinton, Vermont Senator Bernie Sanders and former Maryland Governor Martin O’Malley.

Two Democrats dropped out of the race last week, former Virginia Senator Jim Webb and former Rhode Island Governor Lincoln Chafee.

Vice President Joe Biden also announced he was not entering the 2016 race, giving Clinton a boost that has helped re-establish her as the clear Democratic frontrunner.

Clinton also helped herself with a strong appearance before the House Select Committee on Benghazi and a crisp debate performance the previous week.

In the Republican race, Trump has stepped up his attacks on Carson in recent days, accusing him of having “super-low energy” in an interview with CNN.

Carson responded on Fox that he didn’t want to “get in the mud pit” with Trump, but that may be harder to avoid in Wednesday’s debate.

Carson has pulled ahead of Trump in three recent polls of Iowa Republican voters and holds second place in several national polls.

Trump has not hesitated to go after rivals previously, targeting Bush, Rubio and Paul both in campaign speeches and in past debates. But there may be more of a risk for Trump attacking Carson, who is the best-liked of the Republican contenders, according to recent polls.

But Trump did well in a new Associated Press-Gfk poll where seven in 10 Republicans surveyed said Trump was the party’s strongest general election candidate, compared to six in 10 for Carson.

Republican presidential candidate Donald Trump gestures while speaking at a town hall meeting at Atkinson Country Club in Atkinson, N.H., Oct. 26, 2015.

Sixty percent also said Bush could win the general election while 54 percent said the same about Rubio.

Trump also got a boost recently when Politico reported that 81 percent of Republican insiders who they check with regularly believe that the odds of Trump winning the nomination have grown measurably over the last two months.

Trump’s success continues to stir worry among members of the Republican establishment.

Republican strategist Karl Rove, a key advisor to former President George W. Bush, wrote in the Wall Street Journal that Republicans may have to choose between a nominee who has a conservative agenda or one “reflecting populist anger,” presumably referring to Trump.

Rove warned that “conservative principles” would provide a path to victory while “populist outrage alone will end in defeat.”

Jim Malone has served as VOA’s National correspondent covering U.S. elections and politics since 1995. Prior to that he was a VOA congressional correspondent and served as VOA’s East Africa Correspondent from 1986 to 1990. Jim began his VOA career with the English to Africa Service in 1983.